Many mobile electronic devices such as hand-held computers, cellular telephones, personal digital assistants (PDAs), have a multi-component assembly housed within a small case or housing. A small housing means that a small change (numerically) in the size of the internal components or the housing can result in a large change (in terms of percentage) in the space within the housing allocated for the component assembly. A typical component assembly is a component stack that includes a display, such as a liquid crystal display (LCD) and a circuit board.
Typically, the housing consists of two mating halves to contain the assembly. The mated halves define an interior cavity and, of course, the depth of the component assembly must be slightly less than the depth of the interior cavity. The difference in depth results in an undesirable gap between the component assembly and the housing inside the assembled device.
The gap can be expected to vary in depth due to manufacturing tolerances, assembly tolerances, substitution of components in the component assembly, redesign of the component assembly or the use of a standard housing for different models or devices.
The gap is undesirable since it can result in movement or play of the interior components of the device allowing components to become displaced, disconnected, damaged or simply rattle around inside the housing, especially if the device suffers a shock such as from being dropped.
To eliminate these undesirable results, one solution is to employ a cushion or spacer, for example, a layer of compressible foam. Initially, the uncompressed spacer is deeper than the dimension of the gap so that when the depth of the spacer is added to the depth of the component assembly, the total depth is greater than that of the interior of the housing. However, during assembly of the housing of the device, the interior of the housing comes into contact with the spacer and compresses it against the component stack. Accordingly, the gap is occupied by the compressed spacer preventing movement of the component assembly in the direction of the stack-up (normal to the plane of the circuit board or the LCD).
If the spacer is insufficiently deep, it will not span the gap even in an uncompressed state or it will provide inadequate cushioning for the component assembly. If the spacer is too deep then upon compression it will exert excessive pressure to the component assembly including the display. In the situation where the display is an LCD module, the LCD itself is sensitive to the pressure applied to it. Pushing it unevenly or with too much force will cause a blemish or distortion to appear in the viewing area. Excessive pressure can also prevent the spacer from properly dispersing the energy of an impact because its ability to deflect has already been used in taking up the tolerance of the small available space and in extreme cases excessive pressure or the inability to deflect a shock can result in breaking of the screen. This is very costly, especially if the screen is an expensive colour LCD.
Any of these scenarios can result in an unacceptable product and increase the cost of manufacturing of mobile devices. Accordingly, it is desirable to provide an improved spacer for use with a component assembly to more controllably fill a gap between the component assembly and the housing.